Visual Basic
适用于:Access 2013、Office 2013
为了在 Microsoft Visual Basic 中处理 ADO 事件,必须使用 WithEvents 关键字声明模块级变量。 该变量只能声明为类模块的一部分,并且必须在模块级别声明。 但是,它所受限制并非看起来那样大,因为 Visual Basic Form 对象也是类。 处理 ADO 事件的最简单方式是使用 WithEvents 声明变量。 以下示例将处理 Connection 对象的 ConnectComplete 事件:
' BeginEventExampleVB02
Dim WithEvents connEvent As Connection
Attribute connEvent.VB_VarHelpID = -1
Dim strMsg As String
Private Sub Form_Load()
On Error GoTo ErrHandler:
Dim strConn As String
' Create a new object with event
' handling enabled.
strConn = "Provider='sqloledb';" & _
"Data Source='MySqlServer';" & _
"Initial Catalog='Northwind';" & _
"Integrated Security='SSPI';"
Set connEvent = New ADODB.Connection
connEvent.Open strConn
Exit Sub
ErrHandler:
MsgBox strMsg
End Sub
Private Sub connEvent_ConnectComplete(ByVal pError As ADODB.Error, _
adStatus As ADODB.EventStatusEnum, _
ByVal pConnection As ADODB.Connection)
If adStatus = adStatusErrorsOccurred Then
If Not pError Is Nothing Then
Select Case pError.Number
Case adErrOperationCancelled
' The operation was cancelled in the
' Will event. Notify the user and exit.
strMsg = "I'm sorry you can't connect right now." & vbCrLf
strMsg = strMsg & " Click OK to exit."
Unload Me
Case Else
strMsg = "Error " & Format(pError.Number) & vbCrLf
strMsg = strMsg & pError.Description
strMsg = strMsg & " Click OK to exit."
Unload Me
End Select
Else
strMsg = "Error occured. Click OK to exit."
Unload Me
End If
End If
'frmWait.btnOK.Enabled = True
End Sub
' EndEventExampleVB02
Connection 对象声明于 Form 级别,并使用 WithEvents 关键字来启用事件处理。 Form_Load 事件处理程序实际上通过将新的 Connection 对象分配给 connEvent 来创建对象,然后打开连接。 当然,真实的应用程序在 Form_Load 事件处理程序中会完成比这里更多的处理工作。